Wind turbines have been identified as one of the important ways to generate power from a renewable energy source. Many wind turbine designs have been developed over the last 200 years. The most common type in use commercially today is the horizontal-axis wind turbine (HAWT). The HAWT is generally placed in areas that experience almost continuous wind. The HAWT have propeller blades that turn when the wind blows and the large commercial versions have propeller blades that are as long as 250 feet and the generator sits 650 feet off of the ground. The propeller blades are connected to a shaft that turns a generator which then produces electrical power that is feed into a commercial power grid.
Wind turbine farms have been developed across the world in the last few decades. The wind turbine farms generally use HAWTs to generate power. While the HAWTs are relatively efficient they have their own set of unique problems. It is common to see a wind farm with over 100 wind turbines with less than half of them generating power when the wind is blowing. Most of the problems arise from having the generator mechanism so far off the ground. When a HAWT needs repair it requires large expensive equipment and a skilled technician to repair it. Because of the repair expense, a HAWT often goes without maintenance until enough HAWTs need repair to justify the expense of bringing in a large lift and a technician to repair them. Some of the very large HAWTs have a staircase or elevator built into them so that a technician can get to the working mechanism without a crane. This significantly adds to the cost of the device.
Vertical-axis wind turbines (VAWTs) are another type of wind turbine, which have been around for hundreds of years. While the most common VAWT is named after Finnish engineer Sigurd J. Savonius (circa 1922), there is record of a horizontal wind turbine of the Savonius type being built in 1745 in Furstenburg, Germany by Johann Ernst Bessler. The Savonius VAWT is one of the simplest of wind turbines. The advantage of the Savonius VAWT is that the design allows for placing the power generator that is connected to the VAWT near the ground. Because the axis is vertical and the mechanical power can be transmitted from the top of a tower to the ground level using a vertical shaft. The VAWT does not have to be placed hundreds of feet off of the ground because it does not have large rotating propeller blades. The maintenance of the VAWT is much easier and much less expensive than the maintenance of a HAWT. Another advantage of the Savonius VAWT is that the Savonius VAWT works no matter which direction the wind blows from.
Because of its design, the Savonius VAWT does not need to be aligned with the wind, as is required of a HAWT, in order to capture the wind energy. Thus, in gusty wind conditions where the wind is constantly changing directions, The Savonius VAWT works more effectively that the HAWTs. While there are many locations where there is enough wind on an ongoing basis to justify installing a wind turbine in a commercial or residential setting, placing a HAWT on the top of a building or home that would protrude 100 feet or more above a building or home would be unsightly and difficult to maintain and difficult to receive regulatory permission to install. A VAWT would make more sense than a HAWT, in a small commercial or residential setting, because a VAWT can be placed on top of the roof of a home or building. However, because of the inefficiency of the current VAWT technology, they are difficult to economically justify.
FIG. 1 depicts one embodiment of a prior art Savonius wind turbine 100. While the Savonius wind turbine 100 is simple in concept, and will generate power when the wind blows, the Savonius wind turbine has a significant disadvantage. The concave section 102 of the Savonius wind turbine 100 captures the wind and creates torque in a clockwise direction. The convex side 104, however, creates a torque in the counter clockwise direction. Because the concave side 102 has more drag force than the convex side 104, the Savonius wind turbine 100 turns in a clockwise direction. While the Savonius wind turbine 100 will rotate and produce mechanical power, the drag from the convex side that moves into the wind significantly reduces the efficiency of the Savonius wind turbine 100.
FIG. 2 depicts one embodiment of a prior art vertical axis wind turbine 200 (VAWT) with a vane stop 208. The vane stop 208 will not allow the vanes 204 to rotate in a counter-clockwise direction when the vane shaft 210 reaches the point closest to the source of the wind 108. At this point the vane 204 contacts the vane stop 208 and is forced to turn sideways to the wind providing drag that will turn the turbine in a clockwise direction. The vane 204 in the upper right hemisphere moves into the wind 108. The vanes 204 attempt to line up with the wind 108 to reduce the drag on the side of the VAWT 200 moving into the wind 108. However, since the VAWT 200 is rotating about the turbine shaft in a clockwise direction, the upper vane 204 on the right side is subjected to centrifugal force 206 and the lower vane 204 on the right side is subjected to centrifugal force 212 that cause them to rotate outward in a clockwise direction about the vane shaft 210. The centrifugal forces 206 and 212 can be depicted as acting on the centers of mass 214 of the vanes 204. As can be seen from the drawing, the centrifugal forces 206 and 212 cause increased drag as the vanes 204 move into the wind 108 because the vanes 204 are not lined up directly into the wind 108.